KR101553727B1 - Stirred-tank reactor and method for carrying out a polymerisation reaction using said type of stirred-tank reactor - Google Patents

Abstract

The present invention relates to a method for carrying out a polymerization reaction of unsaturated monomers using a stirred tank reactor and an agitated tank reactor. According to the invention, the stirred tank reactor is characterized in that the product discharge point is designed as a central base outlet, at least partly traversed by the stirrer shaft. The polymerization is carried out continuously under positive pressure such that the stirred tank reactor is operated hydrodynamically.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for performing a polymerization reaction using an agitating tank reactor and an agitating tank reactor of the above type,

The present invention preferably includes a thermostatable reactor jacket, at least one drive agitator shaft, and a stirring and / or shearing element that is non-rotatably connected to the stirrer shaft, preferably at least one The present invention relates to a continuously operated stirred tank reactor for producing a polymer from an unsaturated monomer, in particular comprising at least one starting material feeder and preferably at least one product outlet at the bottom of the location of use. The present invention also relates to a process for carrying out the polymerization reaction from unsaturated monomers using a stirred tank reactor of the type described above.

An agitated tank reactor of the type mentioned above for carrying out the polymerization reaction at a rapid reaction rate in a high-viscosity reaction medium is disclosed, for example, in DD 294 426 A5. The stirred tank reactor disclosed in the patent has a thermostatable reactor jacket and a rotor centered symmetrically in the reactor. The rotor includes a rotor shaft, a yoke having a passageway, and an agitator cylinder that is open at the top and bottom and extends axially of the rotor shaft from the bottom of the reactor to the reactor lid. An annular space between the stirrer cylinder and the reactor jacket and an annular space between the stirrer cylinder and the inserted tube are provided in the spiral stirrer. The stirrer cylinder has a yoke with a passage. The mixing element is arranged between the passages above and below the yoke. Mixing and homogenization of reactants and heat removal are referred to as being improved by a particular arrangement of mixing elements or passages on the yoke of the stirrer cylinder.

In particular, the transport of the product stream is achieved by the formation of a mixing element as a spiral stirrer.

The stirred tank reactor according to DD 294 426 A5 is designed to operate only when the reactor is fully charged. The mixing element should be arranged to avoid deposits on the reactor lid. In addition, the mixing element should be designed such that effective transport of the product stream can be achieved.

Particularly, in the case of a continuously operated reactor, partial charging has the disadvantage that polymer deposits may occur in the gas-filled upper vessel region. In the case of partially charged continuous-running reactors, a discharge pump is typically required, which is very expensive, especially at high throughputs of several thousand kg / h of viscous liquid. During start-up and shut-down of the reactor, reactor contents having a very different viscosity compared to stationary operation should normally be released. The discharge pump can be shut off very quickly due to a lack of lubrication, especially at low viscosities.

Known continuous-running stirred tank reactors are often operated only when partially charged. A leveling device is required for this operation of the stirred tank reactor. Which is relatively sensitive to drawbacks due to the formation of polymer deposits.

The patent DE 3 338 736 A1 describes a polymerization process in which a fully charged stirred tank reactor is used. It is true that caking at the upper reactor wall and poor mixing of the backflow monomer condensate are prevented thereby. However, since the metering addition is not carried out directly beneath the axial face seal, there may be accumulation of polymer therein, which may eventually lead to failure of the agitator. Because the operation is carried out at a slight excess of pressure, expensive and maintenance-expensive gear pumps are also used at the bottom of the reactor, which can exhibit significant wear and failure at low viscosities. In addition, the stirrer does not have a step bearing so that the shaft must be made stronger and the stirrer is sensitive to the imbalance caused by the accumulation of the polymer.

Patent EP 1 122 265 B1 describes a polymerization reactor having a plurality of entrances for the starting material. However, none of the feedstocks are used for flushing the axial face sealant region, so the described drawbacks can occur.

Patent RU 2114869 C1 describes a continuous bulk polymerization process in which a fully charged stirred tank reactor is used. However, in this patent, similarly, the metering addition is not carried out in the vicinity of the axial face seal material, and no step bearing is used, so that the aforementioned adverse effects are expected as well. The recycled cooling polymer solution is fed to the reactor at the second metering addition point without initiator mixing. As a result, the uniformity of the initiator concentration in the reactor is not substantially improved thereby.

It is therefore an object of the present invention to provide a simply designed stirred tank reactor of the type referred to in the preamble, which can be operated continuously when fully charged by simple means. In particular, the reactor should be designed so that it is possible to omit expensive syrup pumps and level controls for high viscosity liquids.

In addition, the supplied starting materials must be mixed with the viscous reaction mixture in the reactor and distributed uniformly as quickly as possible.

According to the invention, this object is achieved in particular by means of a device comprising a thermostatable reactor jacket, at least one drive stirrer shaft and stirring and / or shearing elements that are non-rotatively connected to the stirrer shaft, And one or more product discharge portions at the bottom of the use position, in particular for the production of polymers from unsaturated monomers, wherein the stirred tank reactor according to the invention is particularly suitable for the production of the product discharge , And a form of a central lower outlet through which the stirrer shaft at least partially passes.

In this way, the stirred tank reactor according to the present invention can be fully charged and can be operated under superatmospheric pressure. The pressure in the reactor is applied by the transport member of the starting material, which ensures that the product flows from the reactor to the discharge pipe due to its transport properties. Therefore, the discharge pump for the product mixture can be omitted.

In a suitable modification of the stirred tank reactor according to the invention, it is conceivable to feed one or more starting materials supplied to the reaction space directly into the stirrer shaft inlet area at the top of the use position. For example, the starting material supply may be provided directly under the upper shaft packing.

In the case of a hydrodynamically charged reactor, this makes it impossible for reaction products to enter the shaft seal. The lower portion of the upper shaft seal is flushed with successive washings of the starting material stream. A hydrodynamically charged reactor is interpreted to mean a reactor fully charged with liquid without a gaseous phase.

In a preferred variant, the stirrer shaft is considered to form part of the lower outlet at its end, which is at the bottom of the use position.

For example, the stirrer shaft may be formed as a hollow shaft in communication with the reaction space, at least at its end through the lower outlet.

It is particularly advantageous when the lower outlet portion is in the form of a step bearing for an agitator shaft.

In a further embodiment, the step bearing of the agitator shaft may also be arranged by a bearing block at a certain height above the lower outlet.

The following described advantages of the additional step bearing are maintained.

Conveniently, the step bearing in the form of a sliding bearing can be cooled and lubricated by the reaction mixture.

By appropriate development of the stirred tank reactor according to the present invention it is possible to ensure that the bearing clearance of the step bearing is made into a dimension through which the reaction mixture can flow.

It is particularly advantageous if the end of the stirrer shaft passing through the bottom outlet has an outline in the form of a bearing journal, at least partly flattened. Therefore, the reaction mixture inevitably flows through the entire step bearing including the bearing gap.

Since the stirrer shaft additionally has a step bearing, it is possible to make the diameter of the shaft smaller than that required in the case of an agitator shaft fixed only on the bearing at the top of the use position. Thus, step bearings are intended to avoid unacceptably large deflections of the shaft, for example when an imbalance due to polymerization deposits in the reactor is introduced into the shaft.

In an advantageous modification of the stirred tank reactor according to the invention, it is contemplated that the stirrer shaft has one or more outlet channels that open into the reaction space and extend at least partially in their longitudinal axis in the transverse direction. A transverse hole can be easily provided on the stirrer shaft, for example a step bearing, at least in the form of a common shaft at its lower end.

The above-mentioned object is also achieved by a method for carrying out a polymerization reaction from an unsaturated monomer using the above-described stirred tank reactor, wherein the supply of the starting material and the release of the product are carried out continuously in the reactor .

The polymerization is preferably carried out under superatmospheric pressure.

The established super-atmospheric pressure may be, for example, a super-atmospheric pressure greater than 5 bar relative to atmospheric pressure.

The reactor is conveniently operated with a hydrodynamic charge, i.e. the release of the product from the fully charged reactor is carried out solely by the pressure of the introduced starting material.

In addition to metering addition of the starting material directly below the upper shaft seal, it is advantageous if an additional starting material stream is fed additionally. It is particularly advantageous if the additional starting material stream is introduced into the central region of the reactor by means of one or more metered addition lances. This avoids, for example, poor mixing areas, especially where the initiator concentration is particularly low. Thus, a uniform distribution of the starting materials in the reactor can be achieved by metered addition lances. This is particularly important for initiators that are rapidly degraded for polymerization. In this case, the rapid decomposition means that the half life of the initiator is within the mixing time range of the stirrer. This means about 1 to 200 seconds. When introducing some of the initiator, the segregation with respect to the initiator concentration in the reactor is minimized.

Due to the hydrodynamic operation of the reactor according to the invention, there is in particular no need for a complicated internal structure for transporting the reaction mixture, and this internal structure will interfere with the use of the metered addition lance.

It is particularly appropriate if the metering addition of the starting material is carried out at two or more points of the reactor spatially separated from each other. By distributing the metered addition over a number of metering addition points, better utilization of the reaction volume is possible.

It is generally not possible to uniformly utilize the entire reactor volume as a reaction space in the same part in a continuous operation stirred tank reaction for polymerization. The greater the difference in viscosity between the reactor metered addition and the reactor contents, the greater the tendency to separate. Usually, poor mixing zones occur at various points within the reactor, near the reactor wall, or within the reaction mixture. By virtue of the additional metering addition point, the available reaction volume is increased effectively and the mixing path is kept short. This effect is evidenced especially when the time constant of the reaction is about one order of magnitude different from the mixing time of the stirrer. In this case, the reactants are better distributed throughout the reaction space before the reaction.

Some of the starting materials may be mixed together before entering the reaction space. For example, the initiator fed to the process may be introduced as a dilute solution or in pure form into the monomer metering addition pipe of the reactor prior to the reactor. During the course of the reactor, the initiator is mixed in the monomer pipe. The metering addition point of the initiator is suitably a distance away from the reactor such that a homogeneous initiator / monomer mixture can be formed.

To improve the mixed addition of the initiator, a static mixer may be installed in the monomer metering addition pipe.

The advantage of this procedure is that the concentration gradient of the starting material in the reactor is as small as possible.

Preferably, the jacket temperature of the reactor is adjusted to be at least 10 DEG C higher than the glass transition temperature of the polymer in the reaction solution. This reduces the tendency to form polymer deposits on the low temperature reactor walls.

BRIEF DESCRIPTION OF THE DRAWINGS [

Embodiments of an agitated tank reactor according to the present invention are described below with reference to the accompanying drawings.

1 shows a schematic view of an agitated tank reactor according to the present invention.

2 shows a cross-section through a step bearing of an agitating tank reactor according to the present invention.

The stirred tank reactor 1 shown in FIG. 1 preferably comprises a two-part reactor jacket 2 surrounding the reaction space 3. The stirrer shaft 4, which is non-rotatably connected to the mixing and shearing element 5, passes through the reaction space 3. The mixing and shearing element 5 may be formed in a manner known per se as a rod, spiral or paddle.

The stirrer shaft 4 can be driven directly or indirectly, and in the described embodiment the stirrer shaft is driven directly by the motor 6 with the intermediate gear 7. Below the gear 7, the stirrer shaft 4 is sealed from the reaction space 3 by means of the axial face seal 8. In the described embodiment, the reactor jacket 2 is double walled in each case and consists of two shells 9a and 9b which are arranged together on the side of the all-round flange 10, .

During the operation of the stirred tank reactor 1, the heat exchange medium flows through the reactor jackets 9a, b and the thermostatic conditioning of the heat exchange medium in the reaction space 3 through the reactor jacket is achieved. It may be a heating or cooling medium, for example a thermostatted fluid such as steam, water, heat transfer oil or another heat transfer medium.

The stirrer shaft 4 is fixed at its end on the circle from the motor 6 in the step bearing 11 and the step bearing 11 simultaneously forms the lower central outflow of the stirred tank reactor 1. The formation of the stirrer shaft 4 in the area of the step bearing 11 and the step bearing 11 is shown in Fig.

Please refer to Fig. 2 for the sake of brevity.

The bearing journal forming end of the stirrer shaft 4 passes through the opening 12 in the reactor jacket 2 and the opening forms the lower central outlet of the stirred tank reactor 1. As described below, the openings 12 simultaneously function as a polymer releasing portion. There is provided a sliding bush 14 for receiving the stirrer shaft 4 below the exit gap 13 to form bearing clearance 16 with a typical dimensional tolerance. Thus, the openings of the central product outlet and the diameters of the slide bushes 14 may be the same or different.

The end 15 of the sliding bush 14 on the discharge side is in the form of a liquid outlet and is connected to a product discharge pipe (not shown).

The end of the stirrer shaft 4 partially secured in the sliding bush 14 may be constant in diameter or may vary in diameter within the sliding bush 14. The diameter change of the sliding bush 14 in the axial direction is also conceivable. The end of the stirrer shaft 4 is formed as a bearing journal in the sliding bushing, wherein it is additionally possible to provide one or more flush areas around the stirrer shaft.

The bearing clearance 16 of the stirrer shaft allows the bearing bushes to be lubricated and flushed by the reaction products to be discharged in the sliding bushes.

In the region passing through the step bearing 11, the stirrer shaft 4 is provided with an axial hole 17 communicating with the reaction space 3 through the transverse hole 18. The reaction mixture flows directly into the pipeline that is fed through the transverse holes 18 and the axial holes 17 in the shaft end and connected to the outlet connection piece at the end from the agitator shaft 4. [ The transverse direction holes 17 or the transverse directional holes exist just above the step bearing 11 or above the outlet gap 13. [

Referring back to FIG. The starting material is introduced into the reaction space (3) in the stirred tank reactor (1) through two metering addition points (19a, 19b). The first metering addition point 19a is present directly under the axial face sealant 8. [ The second metering addition point 19b is opened downstream of the first metering addition point 19a in the center of the reaction space 3. At the second metering addition point 19b, a metered addition lance form, not shown, may be provided.

The monomers and / or solvent are fed to the stirred tank reactor 1 via a pipe 20. The chain length regulating agent is added to the monomer via the first metering addition pump 21 and the initiator for initiating the polymerization is metered through the second metering addition pump 22 arranged downstream. Downstream of the initiator metering addition, the starting material stream is branched. The supply to the reaction space 3 is performed through the third and fourth metering addition pumps 23 and 24.

It is also conceivable to omit one or both of the metering addition pumps 23 and 24 and to adjust the distribution of the stream metered into the reactor by valves and / or correspondingly designed pipe sections. A disadvantage of this modification, however, is that a small amount of deposit in the pipeline or valve causes a deviation of the desired proportion of the partial stream in the reactor. It is additionally possible to monitor the starting material stream 19a and / or 19b through a flow meter and regulate it through a control valve.

Reference number list
1 stirred tank reactor
2 reactor jacket
3 reaction space
4 Stirring shaft
5 Mixing and shearing elements
6 Motor
7 Gear
8-axis face sealant
9a, b shell
10 Flange
11 step bearing
12 opening
13 outlet gap
14 sliding bush
15 sliding bushing end
16 Bearing gap
17 axial hole
18 Horizontal hole
19a 1st metering addition point
19b Second metering addition point
20 pipe
21 1st metering pump
22 2nd metering pump
23 Third metering pump
24 Fourth Weighing Pump

Claims (19)

(1) comprising a reactor jacket (2), at least one drive stirrer shaft (4) and at least one stirrer element or shear element that is nonreflectively connected to the stirrer shaft (4) And the product discharge portion is in the form of a lower central outlet through which the stirrer shaft (4) at least partly passes and wherein the stirring tank reactor (1) Characterized in that it comprises a sliding bush (14) for receiving a shaft (4) and the stirrer shaft (4) in the bearing gap is lubricated and flushed by the reaction product ). 2. An agitated tank reactor according to claim 1, characterized in that at least one starting material feed to the reaction space (3) is provided directly to the stirrer shaft inlet region at the top. 3. An agitated tank reactor as claimed in claim 1 or 2, characterized in that the stirrer shaft (4) forms part of the lower outlet at its lower end. 3. An agitator according to claim 1 or 2, characterized in that the stirrer shaft (4) is formed as a hollow shaft in communication with the reaction space (3) at least at its end through the lower outlet Reactor. 3. An agitated tank reactor as claimed in claim 1 or 2, characterized in that the lower outlet is in the form of a step bearing (11) for the stirrer shaft (4). 6. An agitated tank reactor as claimed in claim 5, wherein the bearing clearance of the step bearing (11) is dimensioned to allow the reaction mixture to flow therethrough. 3. An agitated tank reactor as claimed in claim 1 or 2, characterized in that the end of the stirrer shaft (4) passing through the lower outlet has an outline in the form of a bearing journal, at least partially flattened. 3. An agitated tank reactor according to claim 1 or 2, characterized in that the stirrer shaft (4) has at least one effluent channel open to the reaction space and extending at least partially in its longitudinal axis in the transverse direction. A method of carrying out a polymerization reaction from an unsaturated monomer using an agitating tank reactor according to any one of claims 1 to 3, characterized in that the feed of the starting material and the release of the product are carried out in the reactor. The method of claim 9, wherein the polymerization is conducted under an ultra-high pressure. 11. The method of claim 10, wherein an intrinsic atmospheric pressure greater than 5 bar relative to atmospheric pressure is established. 11. The process according to claim 10, wherein the reactor is fully charged with a liquid without a gas phase and is operated. 11. The process according to claim 10, wherein the metered addition of the mixture of starting materials is carried out at two or more points of the reactor spatially separated from each other. 11. The method of claim 10 wherein at least one starting material is introduced into the central region of the reactor through one or more metered addition lances. 11. A process according to claim 10, characterized in that the flow through the reactor takes place in the direction of gravity with respect to the starting material and the product. 11. The method of claim 10, wherein at least some of the starting materials are mixed together prior to entering the reaction space. 11. The method of claim 10, wherein the jacket temperature of the reactor is adjusted so that the jacket temperature of the reactor is at least 5 DEG C higher than the glass transition temperature of the polymer of the reaction solution. The stirred tank reactor as claimed in claim 1 or 2, for producing a polymer from an unsaturated monomer. 3. A stirred tank reactor as claimed in claim 1 or 2, wherein the reactor jacket (2) is thermostable.

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